The present invention relates to a method for the preparation of a spherical hob for generation of an involute gear and also to an apparatus for use in practicing this method.
A cylindrical hob is commonly used for cutting involute, and other, gears. However, a cylindrical hob can be used only for cutting external gears, not internal gears. Internal gears are generally cut by means of a gear cutter having a pinion type cutter. In a very few cases, internal gears are cut by means of a single position hob and single point tool. Gear cutting by means of a pinion type cutter is inferior to hobbing in cutting efficiency and cutting precision. When gears are cut by means of a single position hob or single point tool, cutting precision is not good and the life of the tools is shorter than the life of a cylindrical hob.
It has been found that the disadvantages of the prior art can be overcome by providing a spherical hob for cutting an involute gear. In specific embodiments herein illustrated, the hob is frustospherical, being equally truncated at opposite ends of its axis of rotation due to provision of a bore to receive a shaft the axis of which constitutes the axis of rotation. Since the hob is, nevertheless, in principle, spherical, the term "spherical hob" as employed herein is intended to encompass such frustoconical configurations.
It is a primary object of the present invention to provide a method according to which a spherical hob for cutting an involute gear can easily be prepared.
Another object of the present invention is to provide an apparatus by means of which a spherical hob for generation of an involute gear can easily be prepared.
Other objects and features of the present invention will be apparent from the following embodiments and claims, and many advantages not specifically mentioned herein will also be apparent to those skilled in the art when the present invention is practiced.